1. Field of the Invention
The subject invention is directed to a nozzle for producing a uniform spray of small fluid droplets using a low pressure supply of air and fluid.
2. Background of the Related Art
In the past, the low pressure air available in gas turbine engines and oil burners has been used to assist in the atomization of fuel. The low air pressure in a gas turbine engine generally stems from the engine air circulation, while the low air pressure in an oil burner typically arises from a blower.
The quality of an atomized spray assisted by low pressure air depends on the manner in which the liquid is introduced into the air flow. Most current nozzle designs, for example, U.S. Pat. No. 5,921,470 to Kamath and U.S. Pat. No. 5,086,979 to Koblish et al., have introduced a liquid film into a swirling air flow. In these instances, the liquid film is surrounded by the air flow and sheared into small drops. In the oil burner spray nozzle disclosed in U.S. Pat. No. 5,921,470 to Kamath, the air flow interacts with one side of the liquid film, whereas in the gas turbine spray nozzle disclosed in U.S. Pat. No. 5,086,979 to Koblish et al., the air flow interacts with both sides of the liquid film.
In both instances, the liquid film is generated by several relatively small diameter fluid passages. In particular, in U.S. Pat. No. 5,086,979 to Koblish et al., several radially extending fluid passages deliver oil to an annular atomizing chamber. Similarly, in U.S. Pat. No. 5,921,470 to Kamath, several circumferentially spaced fuel passages deliver fuel to an annular atomizing chamber. In each case, the uniformity of the liquid film produced by the plurality of fuel passages determines the uniformity of the spray pattern. However, the use of several very small fluid passages often results in clogging of the nozzle. Once a fuel passage is clogged, the uniformity of the spray pattern and the operating efficiency of the nozzle are compromised. Consequently, the nozzle must be removed from the operating environment for cleaning or discarded and replaced.
It would be beneficial therefore to provide a low pressure spray nozzle for use in gas turbine or oil burner applications that is adapted and configured to produce a uniform spray pattern of small fluid droplets using a low pressure air and fluid supply, which is not easily susceptible to becoming clogged during use.
The subject invention is directed to a new and useful nozzle for producing a uniform spray of small fluid droplets using a low pressure supply of air and fluid which is particularly well suited for deployment in oil burners and gas turbines. The spray nozzle includes an elongated nozzle body having an axially extending interior chamber defined in part by a tapered distal wall portion. The interior chamber opens into an outwardly tapered exit orifice formed at a distal end of the nozzle body. The nozzle body has at least two radial air inlet ports communicating with the interior chamber, and preferably two diametrically opposed air inlet ports. The air inlet ports communicate with a source of low pressure air.
The nozzle further includes a fluid inlet fitting that is axially disposed within the interior chamber of the nozzle body, and preferably threadably supported therein. The fluid inlet fitting has an axially extending fluid inlet passage which defines a proximal fluid inlet port for communicating with a source of low pressure fluid.
A fluid distribution insert is axially disposed within a distal end portion of the axial fluid inlet passage of the fluid inlet fitting. The fluid distribution insert has an axially extending impact chamber formed therein, and an axial fluid feeding orifice which extends from the impact chamber. The fluid distribution insert further includes a radially inner set of circumferentially disposed air swirling vanes on an inwardly tapered exterior surface thereof. The radially inner set of air swirling vanes impart a rotational component of motion to the low pressure air flowing past the fluid distribution insert.
An air swirling insert is axially disposed within a distal portion of interior chamber of the nozzle body. The air swirling insert has an interior bore for receiving the fluid distribution insert, and an axial fluid mixing orifice communicating with the axial fluid feeding orifice of the fluid distribution insert. The air swirling insert further includes a radially outer set of circumferentially disposed air swirling vanes on an inwardly tapered exterior surface thereof. The radially outer set of air swirling vanes impart a rotational component of motion to the low pressure air flowing between the air swirling insert and the tapered distal wall portion of the interior chamber of the nozzle body.
A fluid metering insert is axially disposed within the impact chamber of the fluid distribution insert. The fluid metering insert has a metering orifice that provides fluid communication between the impact chamber of the fluid distribution insert and the axial fluid inlet passage of the fluid inlet fitting. Preferably, the metering orifice of the fluid metering insert is offset from the axis of the fluid feeding orifice and has a smaller diameter than the fluid feeding orifice of the fluid distribution insert. The offset causes the fluid to impact the front wall of the impact chamber, resulting in decreased fluid velocity. The fluid velocity is further decreased as it flows through the fluid feeding orifice which has a larger diameter than the metering orifice. The introduction of the low velocity fluid into the swirling air provides favorable condition for shearing the fluid into small droplets.
These and other aspects of the low pressure spray nozzle disclosed herein will become more readily apparent to those having ordinary skill in the art from the following description of the drawings taken in conjunction with the detailed description of the preferred embodiments of the invention.